[CMake] Generator expressions containing spaces

[Yves Frederix]

It seems COMMAND_EXPAND_LISTS was indeed the key here. Thanks a lot!

Yves

On Mon, Apr 23, 2018 at 2:11 PM, CHEVRIER, Marc <marc.chevrier at sap.com>
wrote:

> The space is used to separate arguments passed to COMMAND. So your
> generator expression is splitted before evaluation and elements are no
> longer valid generator expression.
>
>
>
> So, to solve your problem, encapsulate the generator expression inside
> quotes. And apply the following advices for correct result:
>
>    - Separate command from args
>    - Use variable to list your arguments and add option
>    COMMAND_EXPAND_LISTS (available with version 3.8) to avoid “spurious”
>    semi-colons in the result
>
>
>
> Your example reworked:
>
>
>
> Set (args foo bar)
>
> add_custom_target(foo)
>
> add_custom_command(TARGET foo POST_BUILD
>
>   COMMAND $<1:echo> "$<1 :${args}>"
>
>   COMMAND_EXPAND_LISTS
>
>   )
>
>
>
>
>
> *From: *CMake <cmake-bounces at cmake.org> on behalf of Yves Frederix <
> yves.frederix+cmake at gmail.com>
> *Date: *Monday 23 April 2018 at 13:08
> *To: *"cmake at cmake.org" <cmake at cmake.org>
> *Subject: *[CMake] Generator expressions containing spaces
>
>
>
> Hi,
>
>
>
> I recently learned that the COMMAND line in a custom command supports
> generator expressions. In particular, what makes this powerful is that if
> the expression evaluates to the empty string, no corresponding code will be
> added to the target (as documented in the docs
> <https://cmake.org/cmake/help/v3.11/command/add_custom_command.html?highlight=add_custom_command>
> ).
>
>
>
> While this works very nicely for single-string command, I fail to make it
> work for commands consisting of multiple space-separated strings:
>
>
>
> ```
>
> ~/tmp/genex_with_spaces$ cat CMakeLists.txt
>
> cmake_minimum_required(VERSION 3.6)
>
>
>
> add_custom_target(foo)
>
> add_custom_command(TARGET foo POST_BUILD
>
>   COMMAND $<1:echo bar>
>
>   )
>
>
>
> ~/tmp/genex_with_spaces$ grep bar build/CMakeFiles/foo.dir/build.make
>                                                 "\$$<1:echo" bar>
>
> ```
>
>
>
> As can be seen, the generator expression is not expanded.
>
>
>
> My question is now whether I am doing something wrong (is there a correct
> way of dealing with spaces in the context of generator expressions?) or
> might this be an inherent limitation of generator expression in general?
>
>
>
> As a workaround, the only thing that seems to work is to put each of the
> space-separated components of the command in (typically identical) genexes:
>
>
>
> ```
>
> ~/tmp/genex_with_spaces$ cat CMakeLists.txt
>
> cmake_minimum_required(VERSION 3.6)
>
>
>
> add_custom_target(foo)
>
> add_custom_command(TARGET foo POST_BUILD
>
>   COMMAND $<1:echo> $<1:bar>
>
>   )
>
>
>
> ~/tmp/genex_with_spaces$ grep bar build/CMakeFiles/foo.dir/build.make
>                                             echo bar
>
> ```
>
>
> Of course, while this works, things becomes very unreadable if the genex
> is more complex.
>
>
>
> Other things that I have tried but failed:
>
>    - escape the space with a backslash -> this quotes the entire
>    expression inside the genex.
>    - define the command directly as a list inside the genex -> this
>    removes spaces between the different components of the command and quotes
>    that result.
>    - treat the command as a list, perform string operations to wrap each
>    element in the desired regex and convert semicolon to spaces -> again
>    results in the command being quoted as a whole.
>
>
>
> Any advice is highly appreciated.
>
>
>
> Thanks,
>
> Yves
>
>
>
>
>
>
>
>
>
>
>
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